movies skip in iTunes and iPhoto

Within the last couple of days, I've noticed that movies on iTunes and movies in iPhoto have started pausing briefly, like the video can't keep up with the audio. The movies will play in their entirety but will pause every five seconds or so. The audio is perfectly fine, but the video is wonky.

Does this sound like a hardware issue, or is this something else?

Anyone have any advice????

Thanks,

Kiffin